Weight-loss surgery isn't risk-free, but a new study suggests that in the hands of a skilled surgeon, it may be safer than previously thought. However, some people -- including those with sleep apnea or a history of blood clots -- are more likely to have problems with surgery than others, according to a study published this week in the New England Journal of Medicine.

Weight-loss surgery is safer, but could cause complications for people with sleep apnea or a history of blood clots.

"The overall conclusion that we reached is that bariatric-surgery safety is actually quite good," said Dr. Bruce Wolfe, a professor of surgery at the Oregon Health and Science University.

In the past, bariatric procedures have been associated with death rates of 2 to 3 percent and complication rates of up to 24 percent. However, the obesity epidemic is fueling a rise in such surgeries, prompting concerns about their safety. In 2005, 171,000 people underwent bariatric surgery, more than 10 times the number that had the procedure in 1994.

To assess the safety of such operations, Wolfe and his colleagues looked at 4,776 patients in the first month after having a bariatric procedure. They found that 4.3 percent of patients had a serious problem, such as a blood clot or needing another operation, and 0.3 percent, or 15 patients, died within a month after surgery -- a complication rate similar to other types of surgery.

Sleep apnea is a common disorder in the obese (about half of the patients in the study had the condition). Excess weight in the neck region can contribute to sleep apnea, which is characterized by snoring and the collapse of the upper airway during sleep, sometimes hundreds of times a night.

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Sleep apnea causes sleepers to snort and gasp for breath and is associated with high blood pressure, vascular changes, and a greater risk of heart disease. "We assume (the effects) are related to why it is a surgical risk," Wolfe says.

Surgeons at Brigham and Women's Hospital, in Boston, Massachusetts, have been performing bariatric surgery with good results since 1995, said Dr. Malcolm Robinson, an assistant professor of surgery at Harvard Medical School, who practices at the hospital and wrote an editorial accompanying the study. "As the art of bariatric surgery has evolved, it's become safer, and this study is proof of that evolution," he said.

Even with the risks of an operation factored in, bariatric surgery can be a lifesaver, particularly for people who are very obese. Such patients are at high risk of death due to obesity-related illnesses, such as heart disease and type 2 diabetes. Such surgery is recommended only for those with a body mass index greater than 40, which would be 248 pounds or more for someone who is 5 feet 6 inches. If other health problems, such as diabetes, are present, surgery may be recommended for someone with a BMI of 35 or higher (217 pounds or more for someone who is 5 feet 6 inches). Health.com: The slimming power of mint

"[Research suggests that] surgery increases survival and makes people live longer, even taking into account mortalities," said Wolfe.

The patients in the new study were treated between 2005 and 2007 at 10 centers with a large volume of bariatric procedures. In all, 33 highly skilled surgeons, who were certified by the Longitudinal Assessment of Bariatric Surgery Consortium, conducted the operations. Robinson says that the study's low complication rate might not be the standard at all centers.

Plus, the study could not determine if one type of bariatric procedure was better than the others. Most of the patients had one of three procedures: an open Roux-en-Y, in which a small pouch is created that bypasses the stomach and attaches to the upper intestine; a Roux-en-Y conducted laparoscopically, in which a camera, light, and instruments are threaded through a small incision; or laparoscopic adjustable gastric banding, in which an adjustable band is wrapped around the stomach to create a small pouch, which then empties into the larger portion of the stomach.

The death rate was 2.1 percent with the open Roux-en-Y and 0.2 percent with the laparoscopic version. (Some patients who underwent the open Roux-en-Y had health factors that put them at greater risk for complications.) There were no deaths associated with laparoscopic adjustable gastric banding.

Some doctors avoid using the adjustable band procedure because they think it needs to be adjusted or removed too often, and because they believe the weight-loss results aren't as strong, according to Robinson. Others prefer it, saying it's safer and just as successful in terms of pounds lost.

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Patients who have experienced blood clots prior to the surgery were more prone to having them again, regardless of the kind of operation, said Wolfe. He said that the increased risk of complications in patients who were so heavy they couldn't walk was not surprising.

"It's believed to be important that after surgery, patients walk around to reduce blood clots," Wolfe said. "But if a person is unable, they presumably are at a higher risk for blood clots."

He recommends losing 10 percent of one's body weight before surgery to help speed recovery. "[But] a low BMI didn't automatically mean the complication rate is lower," he cautioned. "Other factors are involved."

When choosing a hospital for the surgery, experts recommend considering the center's expertise, equipment, dietary program, nonphysician health-care providers, and the anesthesiologists' skill and experience (it is harder to administer anesthesia to heavier patients).

The researchers plan to follow 2,400 patients for several years after surgery to determine the long-term complications and benefits of the different procedures.